docs: add experimental software disclaimer

Add prominent warning that this SDK is experimental and not for production use.
Directs users to the ATProto SDK and scaffold app for production.

Changes:
- Add warning banner to root README.md
- Add warning banner to sdk-core README.md
- Add warning banner to sdk-react README.md
- Add runtime console.warn on SDK instantiation

Author: daviddao

README.md

@@ -1,5 +1,11 @@
 # Hypercerts SDK
 
+> **⚠️ Experimental Software — Not for Production Use**
+>
+> This SDK is experimental and under active development. It should **not** be used in production environments. For
+> production use, please use the [ATProto SDK](https://github.com/bluesky-social/atproto/tree/main/packages) directly
+> and the [scaffold app](https://github.com/hypercerts-org/hypercerts-app) as a reference implementation.
+
 A monorepo containing SDK packages for the Hypercerts protocol on ATProto.
 
 ## Packages

packages/sdk-core/README.md

@@ -1,5 +1,11 @@
 # @hypercerts-org/sdk-core
 
+> **⚠️ Experimental Software — Not for Production Use**
+>
+> This SDK is experimental and under active development. It should **not** be used in production environments. For
+> production use, please use the [ATProto SDK](https://github.com/bluesky-social/atproto/tree/main/packages) directly
+> and the [scaffold app](https://github.com/hypercerts-org/hypercerts-app) as a reference implementation.
+
 Framework-agnostic ATProto SDK for Hypercerts. Create, manage, and collaborate on hypercerts using the AT Protocol.
 
 ```bash

packages/sdk-core/src/core/SDK.ts

@@ -175,6 +175,13 @@ export class ATProtoSDK {
     // Initialize OAuth client
     this.oauthClient = new OAuthClient(configWithDefaults);
 
+    // Experimental software warning
+    console.warn(
+      "[@hypercerts-org/sdk-core] ⚠️ This SDK is experimental and should not be used in production. " +
+        "For production use, please use the ATProto SDK (https://github.com/bluesky-social/atproto) " +
+        "and the scaffold app (https://github.com/hypercerts-org/hypercerts-app).",
+    );
+
     this.logger?.info("ATProto SDK initialized");
   }
 

packages/sdk-react/README.md

@@ -1,5 +1,11 @@
 # @hypercerts-org/sdk-react
 
+> **⚠️ Experimental Software — Not for Production Use**
+>
+> This SDK is experimental and under active development. It should **not** be used in production environments. For
+> production use, please use the [ATProto SDK](https://github.com/bluesky-social/atproto/tree/main/packages) directly
+> and the [scaffold app](https://github.com/hypercerts-org/hypercerts-app) as a reference implementation.
+
 React hooks and components for the Hypercerts ATProto SDK.
 
 ```bash